The conventional dumbbell is integrally made of a metal material by casting. The weight of the conventional dumbbell is fixed. As a result, it is necessary to purchase a number of dumbbells of various weights.
The conventional adjustable dumbbell comprises a grip bar and a plurality of weights which are fastened with both ends of the grip bar. The dumbbell can be adjusted in weight by adjusting the number of the weights that are fastened with both ends of the grip bar. However, the conventional adjustable dumbbell is defective in design in that the weights are of a disklike shape, and that the dumbbell is prone to move about on the surface to inflict a wound on one's toes.
With a view to overcoming the drawbacks of the conventional adjustable dumbbell described above, a Taiwanese Patent discloses an adjustable dumbbell comprising a main body having a support plate which is provided in two sides thereof with a slot into which a fastening pin is inserted. By changing the position of the fastening pin, the weight of the dumbbell can be adjusted. The weights are rectangular so that they are not prone to roll on the surface. However, the fastening pin is susceptible to deformation, thereby making the weights vulnerable to becoming unfastened with the connection rod of the weights. The weights are likely to fall on the ground at the time when the dumbbell is in use.